Evening star. [volume] (Washington, D.C.) 1854-1972, 1887-08-27
Lightning.
THE MORE COMMON KINDS CONTRASTED WITH THE
SHEET AND THE GLoBULAR.
Lightning.


SHEET AND THE GLOBULAR.
From Chambers Journal
Every one is familiar with the fact that light
ming does not spring direct from cloud to cloud or
to the earth, but pursues zigzag course This is
Que to the fact that the air Is not equally humid
throughout Electricity always takes the path
which offers least resistance to its passage Damp
air is a much better conducting medium than dry
air, consequently the lightning selects the damp
est route avoiding the drier strata and zones it
encounters, and advances, now directly, now
Obliquely, until IL reaches the opposite cloud
where 1t subdivideS into number OF forks. owing
TO the resistance 1t encounters in its path intense
heat Is generated which causes the air to expand.
Immediately after the flash the air again con-
tracts with great violence and with loud report
which Is echoed and re-echoed among the Clouds
varying distances is drawn out into series. and
being still further prolonged by the echoes, the
ron OF the thunderis produced II is curious fact
tnat although the sound OF thunderi is exceedingly
loud when heard near at hand, the area over which
IL Is audible Is comparatively circumscr1bed. The
noise OF a cannOnade will be heard under favOra-
Die conditions at a distance OF nearly 100 miles
while the sound OF thunder does not travel Is
miles.
The occurrence OF the thunder and the lightning
IS OF course simultaneous; but light travels
faster than sOund-itS passage Is practically in
stantaneou&the flash may be seen several sec
onds before the thunder is heard. The distance OF
thunder may thus be approximately estimated,
an interval OF five seconds betWeen the flash and
the thunder clap being allowed to each mile.
lame moinentarlly illuminating part OF the sky or
cloud surface 1t is In reality but the reflection OF
lightning flashing beyond the horizon or behind
the clouds, and at too great distance for the
thunder TO be audible.
But the most remarkable OF all the manifesto
tons OF electricity is globular lightning, in APP
pearance like BAN OF fire moving eisureiy along
and remaining visible 1t may be, for several min
utes- Many curious accounts are related OF its
VagarleS. One OF the most interesting and circum-
stantlai is that given by Mr.. Fitzgerald, County
DONEGAL Ireland, who saw globe of fire slowly
descend from the Glendowan Mountains to the
valley below. Where IL first touched the ground
IL eXcavated hole about 20 feet square 'sas IL it
had been cut out with huge knife" This was
scarcely the work OF a minute.
For a distance OF twenty perches it plowed
trench about TOUR feet deep, and, moving along
the bank OF stream, IL made u rurrOW q foot In
depth: Finally It tore away part OF the bank five
percheS In length and five feet Deep and "nuring
the immense mass into the bed OF the stream, it
new into the opposite peaty bank" The globe
was Visible twenty minutes, and traversed dis
lance OF mile, showing that its progress was
for lightning, very slow indeed. During thunder
storms OF extreme violence on Deeside balls OF fire
are occasionally seen TO roll down the sides Of
Lochnagar, which are, no doubt, Identical with
globular lightning.